The present invention is directed to a process for forming two-color images. More specifically, the present invention is directed to a process for forming two-color images which comprises charging an imaging member, creating on the member a latent image comprising areas of high, medium, and low potential, developing the low areas of potential with a colored developer comprising a first blue colored toner, a second cyan colored toner, and a specific "color" carrier as described herein, subsequently developing the high areas of potential with a black developer comprising a specific black toner and a specific "black" carrier as described herein, transferring the developed two-color image to a substrate, and optionally permanently affixing the image to the substrate.
The process of charging a photoresponsive imaging member to a single polarity and creating on it an image consisting of at least three different levels of potential of the same polarity is disclosed in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference. This patent discloses a method of creating two colored images by creating on an imaging surface a charge pattern including an area of first charge as a background area, a second area of greater voltage than the first area, and a third area of lesser voltage than the first area, with the second and third areas functioning as image areas. The charge pattern is developed in a first step with positively charged toner particles of a first color, and, in a subsequent development step, developed with negatively charged toner particles of a second color. Alternatively, charge patterns may be developed with a dry developer containing toners of two different colors in a single development step. According to the teachings of this patent, however, the images produced are of inferior quality compared to those developed in two successive development steps. Also of interest with respect to the tri-level process for generating images is U.S. Pat. No. 4,686,163.
U.S. Pat. No. 4,948,686, the disclosure of which is totally incorporated herein by reference, discloses a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential with a developer comprising a colored first toner comprising a first resin selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a first pigment; a charge control agent; colloidal silica surface external additives present; and external additives comprising metal salts or metal salts of fatty acids; and a first carrier comprising a core and a coating selected from the group consisting of methyl terpolymer, polymethyl methacrylate, and a blend of from about 35 to about 65 percent by weight of polymethylmethacrylate and from about 35 to about 65 percent by weight of chlorotrifluoroethylene-vinyl chloride copolymer, wherein the coating contains from 0 to about 40 percent by weight of the coating of conductive particles; (4) subsequently developing the high areas of potential with a developer comprising a black second toner comprising a second resin present selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a second pigment; and a second charge control additive; and a second carrier comprising a core and a coating selected from the group consisting of chlorotrifluoroethylene-vinyl chloride copolymer containing from 0 to about 40 percent by weight of conductive particles; polyvinylfluoride; and polyvinylchloride; and (5) transferring the developed two-color image to a substrate.
U.S. Pat. No. 4,264,185, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for forming two color images by forming a bipolar electrostatic image of a two color original document on a photoconductive drum. A first developing unit applies a toner of a first color and polarity to the drum and a second developing unit applies a toner of a second color and polarity to the drum to form a two color electrostatic image which is transferred and fixed to a copy sheet. A bias voltage of the first polarity is applied to the second developing unit to repel the toner of the first color and polarity against the drum and prevent degradation of the first color toner image. A bias voltage of the second polarity is applied to the first developing unit to prevent contamination of the first color toner with the second color toner.
U.S. Pat. No. 4,308,821 discloses a method and apparatus for forming two-color images which employs two magnetic brushes. The first developed image is not disturbed during development of the second image, since the second magnetic brush contacts the surface of the imaging member more lightly than the first magnetic brush, and the toner scraping force of the second magnetic brush is reduced in comparison with that of the first magnetic brush by setting the magnetic flux density on a second non-magnetic sleeve with an internally disposed magnet smaller than the magnetic flux density on a first magnetic sleeve, or by adjusting the distance between the second non-magnetic sleeve and the surface of the imaging member. In addition, the toners may have different quantities of electric charge.
U.S. Pat. No. 4,378,415 discloses a method of highlight color imaging which comprises providing a layered organic photoreceptor having a red sensitive layer and a short wavelength sensitive layer, subjecting the imaging member to negative charges, followed by subjecting the imaging member to positive charges, imagewise exposing the member, and developing with a colored developer composition comprising positively charged toner components, negatively charged toner components, and carrier particles.
U.S. Pat. No. 4,430,402, discloses a two-component type dry developer for use in dichromatic electrophotography which comprises two kinds of developers, each of which consists of a toner and a carrier. Dichromatic images are formed by developing a both positively and negatively electrified electrostatic latent image successively with toners different in polarity and color from each other, wherein one carrier becomes positively charged by friction with either of the two toners while the other carrier becomes negatively charged by friction with either of the two toners.
U.S. Pat. No. 4,594,302 discloses a developing process for two-colored electrophotography which comprises charging the surface of a photoreceptor with two photosensitive layers of different spectral sensitivities with one polarity, subsequently charging the photoreceptor with a different polarity, exposing a two-colored original to form electrostatic latent images having different polarities corresponding to the two-colored original, developing one latent image with a first color toner of one polarity, exposing the photoreceptor to eliminate electric charges with the same polarity as the first color toner which are induced on the surface of the photoreceptor in the vicinity of the latent image developed by the first color toner, and developing the other latent image with a second color toner charged with a polarity different from that of the first color toner.
U.S. Pat. No. 4,500,616 discloses a method of developing electrostatic latent images by selectively extracting colored grains of one polarity from a mixture containing colored grains having opposite polarity to each other in the presence of an alternating field, followed by development of the electrostatic image by the selectively extracted colored grains.
U.S. Pat. No. 4,524,117 discloses an electrophotographic method for forming two-colored images which comprises uniformly charging the surface of a photoreceptor having a conductive surface and a photoconductive layer sensitive to a first color formed on the conductive substance, followed by exposing a two-colored original to form on the photoconductive layer a latent image corresponding to a second color region in the original with the same polarity as the electric charges on the surface of the photoconductive layer. The photoreceptor surface is then subjected to a reversal development treatment by the use of a photoconductive color toner charged with the same polarity as the electric charges constituting the latent image, to develop the non-charged region with the photoconductive toner. The latent image is then subjected to normal development treatment with an insulative toner having a color different from the color of the photoconductive toner. Subsequently, the color toners on the photoconductive layer are charged with a different polarity from the charging polarity and, simultaneously, the original is exposed through a filter shielding against the first color, thereby forming a two-colored image.
U.S. Pat. No. 4,525,447, the disclosure of which is totally incorporated herein by reference, discloses an image forming method which comprises forming on a photosensitive member an electrostatic latent image having at least three different levels of potentials, or comprising first and second latent images and developing the first and second latent images with a three component developer. The developer comprises a magnetic carrier, a first toner chargeable to one polarity by contact with the magnetic carrier, and a second toner chargeable to a polarity opposite to that of the first toner by contact with the first toner, but substantially not chargeable by contact with the magnetic carrier.
U.S. Pat. No. 4,539,281 discloses a method of forming dichromatic copy images by forming an electrostatic latent image having a first image portion and a second image portion. The first image portion is developed by a first magnetic brush with a magnetic toner of a first color that is chargeable to a specific polarity, and the second image portion is developed by a second magnetic brush with a mixture of a magnetic carrier substantially not chargeable with the magnetic toner and a non-magnetic toner of a second color chargeable to a polarity opposite to that of the magnetic toner by contact with the magnetic carrier.
U.S. Pat. No. 4,562,129, the disclosure of which is totally incorporated herein by reference, discloses a method of forming dichromatic copy images with a developer composed of a high-resistivity magnetic carrier and a nonmagnetic insulating toner which are triboelectrically chargeable. An electrostatic latent image having at least three different levels of potential is formed and the toner and carrier are adhered respectively onto the first and second image portions.
U.S. Pat. No. 4,640,883, the disclosure of which is totally incorporated herein by reference, discloses a method of forming composite or dichromatic images which comprises forming on an imaging member electrostatic latent images having at least three different potential levels, the first and second latent images being represented respectively by a first potential and a second potential relative to a common background potential. The first and second images are developed by a first magnetic brush using two kinds of toners, at least one of which is magnetic, and both of which are chargeable to polarities opposite to each other, with application to a developing electrode of a bias voltage capable of depositing the magnetic toner on the background potential area, to deposit selectively the two toners on the first and second latent images and to deposit the magnetic toner on the background potential area, while collecting the deposited magnetic toner at least from the background potential area by second magnetic brush developing means.
U.S. Pat. No. 3,013,890 (Bixby), the disclosure of which is totally incorporated herein by reference, discloses a method and composition for making visible electrostatic images whereby both positive and negative electrostatic images may be developed simultaneously in one or two colors. The process entails generating an electrostatic image on an insulating surface, bringing to the insulating surface a solid surface having electrostatically coated thereon positively and negatively charged powder particles, whereby the particles are electrostatically attracted from the surface bearing the powder particles to deposit on the insulating surface in conformity with electrostatic lines of force of the electrostatic image. In a specific embodiment, both kinds of toner particles are both coated onto a single carrier and, relative to the carrier surface, the first toner particles assume a positive electrostatic charge and the second toner particles assume a negative electrostatic charge.
U.S. Pat. No. 3,045,644 (Schwertz), the disclosure of which is totally incorporated herein by reference, discloses a two-color electrostatic apparatus for recording and printing information. An electrostatic latent image is applied to an insulating surface, said image having areas of both positive polarity and negative polarity. Subsequently, positively charged and negatively charged toner particles of two different colors are applied consecutively to the latent image to develop the two-color image.
U.S. Pat. No. 4,395,471 (Hauser et al.), the disclosure of which is totally incorporated herein by reference, discloses a developer composition comprising a styrene/n-butyl methacrylate copolymer resin, a colorant, and a single carrier. In one embodiment, the composition is a combination of a single carrier, a cyan toner comprising a styrene/n-butyl methacrylate copolymer resin and a tetra-4-(octadecylsulfonomido)phthalocyanine pigment, a magenta toner comprising a styrene/n-butyl methacrylate copolymer resin and a 2,9-dimethyl substituted quinacridone pigment, and/or a yellow toner comprising a styrene/n-butyl methacrylate copolymer resin and a diaryldide 3,3-dichlorobenzidene aceto acetanilide pigment. A series of toners is provided wherein a variety of single colored toners are obtained by blending different amounts of the primary colors together with the carrier.
U.S. Pat. No. 4,312,932 (Hauser et al.), the disclosure of which is totally incorporated herein by reference, discloses a color developing composition comprising a single carrier and toner resin particles, each toner particle containing up to four pigments. A series of toners is provided wherein a variety of single colored toners are obtained by incorporating different amounts of the pigments into each toner in the series.
Also directed to the tri-level imaging process and specific embodiments thereof are U.S. Pat. No. 4,903,048, U.S. Pat. No. 4,847,655, U.S. Pat. No. 4,811,046, U.S. Pat. No. 5,021,838, U.S. Pat. No. 4,833,504, U.S. Pat. No. 5,079,114, U.S. Pat. No. 5,080,988, and U.S. Pat. No. 4,901,114, the disclosures of each of which are totally incorporated herein by reference.
Copending Application U.S. Ser. No. 07/755,979, entitled "Improved Toner and Process for Forming Two-Color Images," with the named inventors Edward J. Gutman, Michael L. Grande, William H. Hollenbaugh, Jr., and Roger N. Ciccarelli, filed Sep. 6, 1991, the disclosure of which is totally incorporated herein by reference, discloses a toner composition comprising a resin, a colorant, and a charge control additive selected from the group consisting of (a) zinc 3,5-di-tert-butyl salicylate compounds; (b) mixtures of a zinc 3,5-di-tert-butyl salicylate compound and an alkyl pyridinium halide; (c) mixtures of a zinc 3,5-di-tert-butyl salicylate compound and distearyl dimethyl ammonium methyl sulfate; (d) mixtures of a zinc 3,5-di-tert-butyl salicylate compound and distearyl dimethyl ammonium bisulfate; (e) mixtures of an aluminum 3,5-di-tert-butyl salicylate compound and an alkyl pyridinium halide; (f) mixtures of an aluminum 3,5-di-tert-butyl salicylate compound and distearyl dimethyl ammonium methyl sulfate; (g) mixtures of an aluminum 3,5-di-tert-butyl salicylate compound and distearyl dimethyl ammonium bisulfate; and mixtures thereof, a colloidal silica external additive, and a metal salt of a fatty acid external additive. Also disclosed are imaging processes employing the toner, including a process for forming two-color images which comprises creating on an imaging member a latent image comprising areas of high, medium, and low potential, developing the low areas of potential with a developer comprising the toner disclosed herein and a carrier, subsequently developing the high areas of potential with a developer comprising a toner of a second color and a carrier, transferring the developed two-color image to a substrate, and optionally permanently affixing the image to the substrate.
Copending Application U.S. Ser. No. 07/755,915, entitled "Improved Electrostatic Developing Composition and Process", with the named inventors Don B. Jugle, Michael L. Grande, Edward J. Gutman, Douglas A. Lundy, and Charles D. Zimmer, filed Sep. 6, 1991, the disclosure of which is totally incorporated herein by reference, discloses a developer composition which consists essentially of a toner consisting essentially of a resin, a colorant, and colloidal silica external additive particles and a carrier consisting essentially of a core, an optional coating on the core, and an external additive selected from the group consisting of metal salts of fatty acids, linear polymeric alcohols comprising a fully saturated hydrocarbon backbone with at least about 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group, polyethylene waxes with a molecular weight of from about 300 to about 2,000, polypropylene waxes with a molecular weight of from about 300 to about 3,000, and mixtures thereof. Also disclosed are processes for using the aforementioned developer in a tri-level development process.
Copending Application U.S. Ser. No. 07/706,476, entitled "Passivated Toner Compositions," with the named inventors Roger N. Ciccarelli and Denise R. Bayley, filed May 28, 1991, the disclosure of which is totally incorporated herein by reference, discloses a process for the preparation of passivated toners with a substantially stable positive or negative triboelectic value of from about 10 to about 30 microcoulombs per gram which comprises admixing toner resin particles, colored pigment particles, and a charge enhancing additive and subsequently adding thereto surface additives, wherein the charge additive functions primarily as a passivating component. The toners are useful in tri-level processes for creating two-color images in a single pass. Also disclosed is the admixing in known effective amounts of known cyan, magenta, and yellow toners, preferably with a common carrier, to obtain process colors like red, blue, green, and the like.
Copending Application U.S. Ser. No. 07/706,477, entitled "Passivated Green Toner Compositions," with the named inventors Roger N. Ciccarelli and Denise R. Bayley, filed May 28, 1991, the disclosure of which is totally incorporated herein by reference, discloses a green toner comprising resin particles, HELIOGEN GREEN.TM. pigment particles, a charge enhancing additive, and surface additive particles. The toner is useful in tri-level processes for creating two-color images in a single pass. Also disclosed is the admixing in known effective amounts of known cyan, magenta, and yellow toners, preferably with a common carrier, to obtain process colors like red, blue, green, and the like.
Copending Application U.S. Ser. No. 07/705,595, entitled "Magenta Toner Compositions," with the named inventors Roger N. Ciccarelli and Don B. Jugle, filed May 28, 1991, the disclosure of which is totally incorporated herein by reference, discloses a toner comprising resin particles, magenta pigment particles, and surface additive particles comprising a mixture of colloidal silica, metal oxide, and a polymeric hydroxy compound. The toner is useful in tri-level processes for creating two-color images in a single pass.
While known compositions and processes for forming two-color images are suitable for their intended purposes, a need remains for processes for forming two-color images by a tri-level process wherein at least one of the colors can be adjusted for custom applications. Adjusting the color of a toner employed in a tri-level imaging process is generally a complex process that entails more than merely adjusting the concentrations of one or more pigments contained in the toner. For example, some pigments can be compatible with the toner resin for the present purposes only over a limited concentration range. In addition, pigments may have inherent charging characteristics that will result in admix problems when the pigment concentration is changed. Further, if a blend of two or more colors is employed to develop one of the images in a two-color tri-level imaging process, both toners in the blend must become charged uniformly and rapidly to the same polarity and approximately the same charge magnitude so that both toners transfer from the developer housing to the latent image in the desired concentrations during image development. Additionally, the toner or toners employed to develop one image in a two-color tri-level imaging process must not interact with the toner or carrier employed to develop the image of the other color. Thus, a need remains for processes for forming two-color images wherein one of the colors is developed with a mixture of two types of toner particles of different colors which, when blended, form a desired custom color. Further, there is a need for processes for for forming two-color images wherein one of the colors is developed with a mixture of two types of toner particles of different colors which can be blended in varying ratios to obtain a wide range of blends of desired colors. Additionally, there is a need for processes for forming two-color images wherein one of the colors is developed with a mixture of two types of toner particles of different colors which can be blended in varying ratios such that both types of toner particles become charged to the same polarity and obtain similar charge magnitudes. There is also a need for processes for forming two-color images wherein one of the colors is developed with a mixture of two types of toner particles of different colors and wherein the admix times for each type of toner particle are acceptable. Further, there is a need for processes for forming two-color images wherein one of the colors is developed with a mixture of two types of toner particles of different colors and wherein neither toner in the mixture employed to develop one color interacts with the toner or carrier employed to develop the other color. Mutual and deleterious interaction may occur, for example, when the carrier of the developer used second triboelectrically charges against the toner used first; thus, the first image is developed with the first developer and the second image is subsequently developed with the second developer of different color, and during development of the second image, the carrier of the second developer triboelectrically interacts with the image previously developed with the first toner. This interaction can result in removal of some of the first toner from the substrate, causing reduced image density, and can also lead to contamination of the second developer housing with the first toner. A need also exists for a process for forming two-color images wherein the second developer does not react with, or is triboactively neutral to, the first developed image on the photoreceptor. A need also exists for a process for forming two-color images wherein the first developer comprises a mixture of two types of toner particles of different colors and the mixture does not discharge the latent image to be developed by the second developer. Additionally, there is a need for a two-color image formation process wherein the developers are of specified triboelectric charge, charge distribution, and conductivity, and exhibit acceptable admix times and developer lifetimes. Further, there is a need for a two-color image formation process wherein the developers exhibit similar rheological properties, thereby enhancing fusing, and similar cleaning latitudes, thereby enhancing cleaning of the photoreceptor.